Re: Begin phasing out support for Qt 4?

[John W. Eaton]

On 04/02/2018 08:48 PM, Mike Miller wrote:
> On Mon, Apr 02, 2018 at 20:38:42 -0400, John W. Eaton wrote:
> > Is Qt5 required now for a fully functional build?  It seems so, as the new
> > off-screen printing and help features rely on Qt5 features, correct?  If so,
> > maybe it is time to check only for Qt5 by default, and not check for Qt4
> > unless it is explicitly requested on the configure command line?
>
> No, this is not correct. The current stable branch builds with Qt 4.8,
> and I think also 4.6. Yes, the offscreen GL rendering support will be
> disabled. I think Qt 4.8 supports all of the classes needed for the new
> documentation browser, but I have not tested it yet.
>
> I do understand and have helped people debug the confusing situation
> when a mix of Qt 5 and 4 packages are installed, but I don't think the
> automatic fallback to Qt 4 should be dropped for Octave 4.4.
What about having configure fail by default if an incomplete 
installation of Qt5 is found even if Qt4 might work?  I'm thinking this 
might avoid some confusion.  The error message might say something like

  ERROR: An incomplete set of Qt5 libraries and tools appears to be 
installed on your system.  You may fix your Qt5 installation or try the 
configure option --with-qt=4 if you would prefer to use Qt4 libraries 
and tools.

We would only fall back to Qt4 automatically if none of the required Qt5 
libraries and tools are detected.

jwe